Spark plug



Feb. 9, 1937. A. c. HASTINGS. JR

SPARK PLUG Filed Jan. 15, 1936 1 I l I INVENTOR. 60%; 6. 64472;?

A TTORNE Y.

Patented Feb. 9, 1937 UNITED STATES PATENT oer-ice 14 Claims.

This invention relates to a spark plug, for use in connection with internal combustion engines.

One object of the invention is to provide a novel and highly emcient spark plug, possessing self cleaning capabilities which enable the spark plug to be used and to operate satisfactorily, under severe conditions for relatively long periods of time.

A further object of the invention is to provide a spark plug embodying a novel construction of insulation possessing high insulating efficiency and which may be made at minimum expense and in a uniform manner.

A still further object of the invention is to provide a novel and simplified construction of spark plug, in which the spark is discharged in a novel manner adapted for the production of either a better volume of spark at a given voltage, or the production of a satisfactory volume of spark at a reduced voltage, as compared with other spark plugs of which I am aware.

With these general objects in view, and such others as may hereinafter appear, the invention consists in the'spark plug hereinafter described and particularly defined in the claims at the end of this specification.

In the drawing which illustrates the different features of the invention, Fig. 1 is a vertical sectional view of a spark plug embodying the invention; Fig. 2 is a side elevation of the spark plug shown in Fig. 1; Fig. 3 is a vertical sectional view illustrating a modified form of the present spark plug; and Fig. 4 is an elevation, partly in section, illustrating another modification of the invention.

In general, the present invention aims to provide a simplified and novel construction of spark plug, which is more effective in operation and capable of withstanding severe conditions of use for much longer periods of time than other spark plugs of which I am aware.

Referring now to the drawing, the improved spark plug illustrated therein comprises a metal firing pin or electrode l0 extended through and insulated by a tubular insulating member l2 of any suitable insulating material but which may and preferably will comprise a quartz or heat resisting glass tube. The tubular insulating member I2 is enclosed within a protective outer shell comprising a metal sleeve I4 comprising the second electrode of the spark plug surrounding the lower portion of the insulating member l2 and a a second insulating member l6 surrounding the upper portion of the insulating member, and to one end of which the metal sleeve I4 is secured to form a unit therewith. The firing pin or first electrode l0 may and preferably will be cemented within the insulating member l2 and a suitable terminal member l8 provided to permit a lead wire to be electrically connected to the firing pin.

As illustrated in Fig. l the metal sleeve i4 is externally threaded and screwed into a threaded hole in the insulating member I6 and a suitable gasket 22 of lead, asbestos, or other material provided in order to form a gas-tight connection between the insulator l6 and the surface of the insulating member l2.

In the modification illustrated in Fig. 3, the metal sleeve I4 is provided with an enlarged upper end 32.having a knurled or otherwise roughened surface and the second insulating member I6 formed of a moldable insulating material such as a phenol formaldehyde product is molded directly upon the upper end 32 of the metal sleeve to form a unit therewith. The second insulating member and metal sleeve may be cemented to the external surface of the insulator l2 and the latter may also be cemented to the firing pin or electrode Ill. The upper end of the pin I0 is preferably arranged to project above the upper surface of the second insulator l2 to contact with a metal cap member 26 secured to the second insulator as shown.

The upper end of the first electrode or firing pin l0 may be formed as illustrated in Fig. 1 to provide a knob 24 over which a metal cap member 26 may be forced so that the firing pin may be maintained in its operative position by the cap member, and as shown in Fig. 1 the lower edge 21 of the metal cap may be spun over a shoulder 28 on the insulating member I6 to retain the parts in operative position. The cap may be provided with any suitable form of terminal and as illustrated, with a threaded boss 30 for the reception of a nut.

As a result of the construction thus far described, it is possible to construct the present spark plug so that the lower ends of the firing pin l0, insulator l2 and metal sleeve M are in substantially one plane, presenting in effect a solid surface which may be readily cleaned by emery paper or the like. and these parts may conveniently be made of such diameter that a firing gap of standard size may be formed between the end of the central firing pin l0 and the surrounding end of the metal sleeve It, so that in operation sparks arc across and in close proximity to the insulating surface formed by the end of the insulator l2 usually forming in effect a rosette of flame, of relatively large volume to enable the ignition of a maximum amount of the combustible gas in the engine in which the present spark plug may be used.

In the development of high compression internal combustion engines, it has been found that the pressure conditions under which the spark plug is obliged to operate have a serious efiect upon the volume of the arc of flame produced when the spark jumps from one electrode to the other. Experience with the present construction of spark plug has indicated very superior results in the maintenance of a relatively large and adequate volume of flame even when the plug is operated under relatively high pressure conditions, as for example 150# per sq. in. I attribute this result to the fact that in the present plug the spark travels along and in effect creeps along the insulating surface comprising the end of the insulator l2 and accordingly one feature of my invention contemplates a spark plug in which the electrodes are arranged with relation to one another and to the interposed insulation so that in operation the spark traverses across and in substantial contact with the interposed insulating surface. Possibly in operation a smallb'ody of gas will maintain the arc actually separated from the insulating surface across which it travels in jumping from the end of the firing pin H] to the end of the surrounding sleeve, but in any event, the effect seems to have been that the discharge of the spark across the insulating surface diminishes the voltage required, so that to a substantial extent the deleterious effects of high-pressure conditions on the volume of the are are diminished.

An important advantage of the construction of the present spark plug resides in the protection afforded the insulator 12 from overheating. By making the plug small corresponding to the formation of a 25/1000 gap between the firing pin l and the metal sleeve M, the transmission of heat to the main body of the plug is reduced to a minimum, as a major portion of the surface of the lower end of the plug will during operation be in effect water jacketed, or cooled by the engine cooling medium so that rapid dissipation of the heat may be effected. This feature contributes to overcoming difliculties which have heretofore been experienced when attempts have been made to utilize quartz or glass insulators.

In practice the firing pin I0, insulator l2, and metal sleeve I may be fitted as closely as their expansion characteristics will permit, and it is preferred to cement the firing pin I0 within the tubular insulator I2 with any suitable heat resisting cement. ,The outer insulator [6 serves to protect the insulator 12 from breakage, I,

may prefer to provide one or more holes 38 in the insulator IE to permit the circulation of air through an air passage around a substantial length of the insulator l2 in order to further assist in dissipating any objectionable heat which might accumulate in the insulator.

In the modification illustrated in Fig. 4 I may prefer to form the insulator l2 of a tapering shape such as is illustrated and to correspondingly taper the inner surface of the outer metallic sleeve M in order to permit the insulator to be made of maximum strength and thickness at the same time to provide the small gap between the firing pin and the second electrode l4.

From the description thus far it will be observed that in the operation of the present spark plug, the electrodes are arranged with relation to each other to provide the standard or desired gap and to the insulation interposed between them, so that the spark sweeps across the surface of the insulation, thus providing a path of reduced resistance. Also it has been found that the present spark plug possesses the ability to clean from the insulating surface soot, oil or carbon which may deposit thereon, thus enabling the plug to be used under conditions in which prior plugs have quickly become fouled. The reasons for the self-cleaning feature of the present plug are not entirely understood, but it is believed that the corona which is undoubtedly formed and the accompanying corona wind" assists materially in the removal of deposited soot, oil or carbon from the insulating surface between the electrodes.

The present construction of the spark plug is simple, may be manufactured at minimum expense and in its preferred form contemplates a double insulation with the inner insulator composed of an electrically efiicient heat resisting glass such as the borosilica glass now commercially obtainable under the trade name Pyrex.

By the use of the term thin as employed in my claims, I intend to define a thickness of glass sufilciently small that the thickness of the insulating materials now commercially employed between the inner and outer electrodes in the manufacture of spark plugs for the same operating conditions at-least is several times as great.

As a result thereof, efiicient transfer of heat from the inner electrode to the outer member is accomplished.

The glass need only be sufilciently thick to prevent it being punctured by the electrical potential applied between the inner and outer electrodes. Furthermore, the glass is desirably of less thickness than the length of the spark gap between the electrodes as shown in Figure 3 but may be of a thickness somewhat greater than the length of the spark gap as shown in Figure 1.

By the use of the term heat resisting glass as employed in the claims, I intend to embrace quartz as well as borosilica glass such as Pyrex", although obviously it is my intention to embrace other materials as equivalents which have substantially the same functional characteristics when employed in the manufacture of spark plugs.

While the preferred embodiments of the invention have been illustrated and described, it will be understood that the invention may be embodied in other forms within the scope of the following claims.

I Having thus described the invention, what is claimed is:

1. A spark plug comprising an outer metallic member having an elongated bore therethrough, an inner electrode extending through said bore, and a thin layer of heat resisting glass positioned in said bore and substantially filling the space between said electrode and said member to form an electrical insulating element between said electrode and member and to provide for eflicient transfer of heat from said electrode to said member.

2. A spark plug comprising an outer metallic member having an elongated bore therethrough, an inner electrode extending through said bore, a thin layer of heat resisting glass positioned in said bore and substantially filling the space between said electrode and said member to form an electrical insulating element between said electrode and member and to provide for efficient transfer of heat from said electrode to said member, said electrode extending from one end of said member and insulating means forming a seal between said end of said member and said electrode.

3. A spark plug comprising an outer metal member having a tubular bore, an inner electrode passing through said bore, a thin walled tube of heat resisting glass positioned in said bore so as to surround said inner electrode and substantially fill the space between said electrode and member whereby said electrode is electrically insulated from said member and heat is radially conducted from said electrode to said member.

4. A spark plug comprising an outer metallic member having an elongated tubular bore, an inner electrode positioned within said bore, a thin layer of heat resisting glass positioned in said bore between said inner electrode and said member and terminating adjacent one end of said bore to provide a spark gap between said electrode and saidmember, said glass having a thickness not substantially greater than the length of said spark gap so as to provide for efficient transfer of heat from said electrode to said member.

5. A spark plug comprising an outer metallic member having an elongated tubular bore, a thin walled tube of heat resisting glass positioned in said bore and having its outer surface closely adjacent the inner surface of said bore, an inner electrode positioned within said tube and having its outer surface closely adjacent the inner surfaces of said tube so as to substantially fill the space between said electrode and said member, said tube having walls sufficiently thin to provide for efficient transfer of heat between said electrade and member and terminating adjacent one end of said bore to provide a spark gap between said electrode and said member, said tube and electrode extending beyond the other end of said bore, and electrical insulating means forming a seal between said other end of said member and said electrode.

6. A spark plug comprising an outer metallic member having an elongated bore therethrough, an inner electrode extending through said bore, and a layer of heat resisting glass positioned in said bore and substantially filling the space between said electrode and said member, one end of said electrode being exposed to provide a spark gap between said electrode and said member, said layer of glass having a thickness approximately the same as the length of said spark gap.

'7. A spark plug comprising an outer metal member having an elongated bore therethrough, an inner electrode extending through said bore, a thin walled tube of heat resisting glass also positioned in said bore around said electrode, the walls of said tube substantially filling the space between said electrode and said member, said tube having one end terminating adjacent one end of said bore to provide a spark gap between said electrode and said member and the other end projecting from said bore, said inner electrode having a portion projecting from said other end of said tube and a body of phenol-formaldehyde product molded about the projecting ends of said tube and electrode and one end of said member.

8. A spark plug comprising an outer metallic member having an elongated bore therethrough, an inner electrode extending through said bore, a thin layer of vitreous refractory insulating material positioned in said bore and substantially filling the space between said electrode and said member and terminating adjacent one end of said bore to provide a spark gap between said electrode and said member, said layer having a thickness not substantially greater than the length of said spark gap, and a body of insulating material between the portions of said inner electrode and member which are remote from said spark gap.

9. A spark plug comprising an outer metallic member having an elongated bore therethrough, an inner electrode extending through said bore, a thin tube of vitreous refractory insulating material positioned in said bore and substantially filling the space between said electrode and said member, said tube and said electrode being substantially coextensive at the spark end of the plug so as to expose to the heat of the combustion substantially only the end surface of the electrode to reduce to a minimum heating of the electrode.

10. A spark plug comprising an outer metallic member having an elongated bore therethrough, an inner electrode extending through said bore, a thin walled substantially straight tube of vitreous refractory insulating material positioned in said bore and substantially filling the space between said electrode and said member and terminating adjacent one end of said bore to provide a spark gap between said electrode and said member, said layer having a thickness not substantially greater than the length of said spark gap, and a protective insulating body of molded insulating material between portions of said inner electrode and member which are remote from said, spark gap.

11. A spark plug comprising an outer metallic member having an elongated bore therethrough, an inner electrode extending through said bore, a thin walled tube of vitreous refractory insulating material having substantially uniform internal and external diameters and positioned in said bore and substantially filling the space between said electrode and said member and terminating adjacent one end of said bore to provide a spark gap between said electrode and said member, said layer having a thickness not substantially greater than the length of said spark gap, and a protective insulating body between the portions of the inner electrode and member remote from the spark gap.

12. A spark plug comprising an outer metallic member having an elongated bore therethrough, an inner electrode extending through said bore, a thin walled tube of vitreous refractory insulating material havingsubstantially uniform internal and external diameters and positioned in said bore and substantially filling the space between said electrode and said member and terminating adjacent one end of said bore to provide a spark gap between said electrode and said member, said layer having a thickness not substantially greater than the length of said spark gap, and a body of molded insulating material between the portions of said inner electrode and member which are remote from said spark gap.

13. A spark plug comprising an outer metallic member having an elongated bore therethrough, an inner electrode extending through said bore, a thin walled substantially straight tube of heat resisting glass positioned in said bore and substantially filling the space between said electrode and said member and terminating adjacent one end of said bore to provide a spark gap between said electrode and said member, said layer having a thickness not substantially greater than the length of said spark gap, and insulating means between portions of the inner electrode and member remote from the spark gap.

14. A spark plug comprising an outer metallic member having an elongated bore therethrough,

an inner electrode extending through said bore, a

resisting glass positioned in said bore and substantially filling the space between said electrode and said member and terminating adjacent one end of said bore to provide a spark gap between said electrode and said member, said layer havthin walled substantially straight tube of heat ing a thickness not substantially greater than the length of said spark gap, and a body'o't molded insulating material between portions of said inner electrode and member which are remote from said spark lap.

ARTHUR c. nss'rmqsfaa. 

